Dynaco SCA 35 Owners Manual

Page 1

SERIAL NUMBER

dymaca

This number must be men-

tioned in all communications
- . . .
SCA 35 concerning this eqmpment.

STEREO CONTROL AMPLIFIER

Price $1.00

Pulen'ed 929315

Nymca iNC- 3060 Jefferson St Philadelphia, Pa. 19121 U.S.A.

Page 2

CONTENTS

Operation of Controls . . . .................... . l l . 3

connections to Music System ................... 4

. initial Adjustments and Installation ............. .. 5

d, rconnecting'a Center Loudspeaker ................. 5

, connecting Headphones ....................... 6
- TechnicalCircuit Description . . . l 7 ,
I Assembly Instructions ........ _ ................. _9
L 240 Volt Power Transformer ................... L 16 ,

InVCase of Trouble . . . . .17r
Schematic Diagram ........................... 19 -,
, Service and Warranty .................. I ......... 21 '
._,."Par.ts: List ...... . .............................. 21 -,

SPECIFICATIONS

Inputs: 7 pairs: RIAA magnetic phono low level,
magnetic phono high level (50,000 ohms);
Ceramic phono; NAB 71/2 i.p.s. tape head
(100,000 ohms); radio, tape, spare (250,000 ohms)

Outputs: Constant level tape output, 8 and 16 ohm
loudspeaker outputs, center-channel loudspeaker
output, provision for headphone connection.

Controls: Selector, Volume, Balance, Bass, Treble,
StereoiMono Switch, Loudness Compensation
Switch, Filter Switch, Power Switch.

Tone Control Range: : 12 db at 50 cps and 15 kc.

Sensitivity for 2.5 mv at tape head, 4 mv at low level magnetic
Rated Output: phone, 1 volt at high level inputs.

Power Output: 35 watts continuous, 45 watts IHF
Music Power (both channels).

Frequency Response: : 0.25 db from 20 cps to 20 kc.

Power Response: 20 cps to 20 kc without exceeding 1% distortion
within 1 db of 175 watts (each channel).

IM Distortion: Less than 1% at 17.5 watts (each channel).
Less than 0.2% on any input at average
listening levels.

Hum and Noise: 70 db below 10 millivolt input for rated output
on low level inputs.
80 db down on high level inputs.

Tube Complement: 12AX7/ECC83 (2), 7199 (2),
GBQ5/EL84/7189 (4).

Silicon Diodes: 500 MA, 1000 PIV (2).

Power Consumption: 110 watts, 120 volts 60 cycle AC, or 120/240 volts
50/60 cycle AC with optional PB-O28
power transformer.

Special Features: Attractive Champagnegold anodized aluminum
front panel and die-cast knobs; 2 AC convenience
outlets; provision for headphone output or
center-channel level control; center speaker
output; power transformer sealed in special
encapsulating material for coolest,
quietest operation.

Page 18

Both Channels Not Working

Should neither channel function, there is the possibility
that a similar mistake has been made in the wiring to both
sides. This is an unlikely situation, but it should be checked
by visual comparison of the wiring with the diagrams.

Generally, the cause of malfunction of both channels
together lies in the one section of the unit which is com,
mon to both channels 7 the power supply. The checking of
this section is covered earlier.

It is also possible that the unit is working on radio or
other high level input, but not on phono or tapehead. If
this is true for both channels together, then the power
supply wiring which connects to the P011 board should be
checked, as this is the only element common to both chan-
nels in the preamplifier section

One Channel Not Working

If tubes in one channel do not light, the heater circuits
must be checked as described above. Tubes can be inter-
changed between the two sides to see if substitution shows
up a faulty tube. If this cures the bad channel, then evi-
dently the faulty tube has been located.

If it is not a tube which causes the trouble, then it is
necessary to determine whether it is in the preamp section
(the PC-ll} or the amplifier section (the PC-lO). If radio
input is satisfactory while phono is not, then the trouble
is in the P011 section which handles phono and tapehead
inputs, or in the wiring associated with the selector switch.

If no inputs function, then the difficulty is either in the
front panel wiring which includes the tone control sections,
or in the PC-IO section or in the Z-565 output trans-
former which connects to that channel. The wiring of the
front panel must be carefully compared on both left and right
channels. It is possible to redo the wiring and to inter»
change the two PC-lO boards to determine whether the
fault is on one of these. It is also possible to interchange
the Z-565 output transformers to try to isolate the trouble.
However, a fault in the output transformer is most unlikely,
and this should be tried as a last resort.

If both channels work on radio or other high level input,
but only one works on phono or tapehead input, then the
trouble is in either the P011 board or in the selector
switch or in the front panel wiring from selector switch
through the front panel controls. The PC-ll board has both
preamplifier sections in a parallel arrangement, so com,
parison visually of wiring and parts should indicate whether
there is any difference between these sections.

Each section of the selector switch should be identical in
appearance and in wiring. These should be compared care-
fully. The 12AX7s on the PC-ll should be interchanged to
see if one is at fault.

Hum and Noise

If the unit is working, but there is excessive hum or
noise, the first step is to see whether the trouble is in the
SCA»35 or associated equipment. The SCA-35 should be
checked alone, with all other equipment except the speakers
disconnected, and with the cover and bottom plate on the
SCA secured in place, If the bum is reduced without the
other equipment, then it will be necessary to determine
what kind of ground connections are necessary between
equipment to reduce the bum. Sometimes connecting wires
from chassis to chassis are good, sometimes they are harm-
ful. Reversing line plugs on associated equipment may be
helpful. It must be understood that hum which disappears
when associated equipment is disconnected or turned off,
is not a problem of the SCA-35.

18

Hum which persists after other equipment is eliminated
as a source of trouble is generally a result of either faulty
wiring or a faulty tube. Wires which are not positioned as
shown in the diagrams, may be a cause of burn, This is
particularly true for the wires which lead from the PA-774
transformer, since these wires carry AC currents which
may be a source of hum.

If a tube causes the problem, then it is not likely to
appear in both channels simultaneously. If the hum is loud
with the volume control turned .down, then it is most likely
to be associated with the 7199 tube. If it occurs on phono
or tapehead inputs with the volume turned up a bit, then
it is most likely to be associated with the 12AX7 tube for
the channel which shows the hum. These tubes can be
checked by substituting in the other channel.

An objectionable level of hiss is most likely caused by a
defective resistor on a printed circuit board. If it is heard
with the volume turned down, it is likely to be part of the
7199 circuit - it can often be located by wiggling the body
of the resistor (using insulated pliers) to see if the hiss is
affected. If it is on phono or tapehead input, with volume
turned up, then the same possibility applies to the 12AX7
circuit.

Some hum and hiss will always existfidepending on
speaker efficiency and other factors. However, it should be
negligible at normal listening levels. At very high levels,
some noise will always be audible, but of course this will be
masked by the loud sound. With the volume control at
minimum, noise with a shorted input should be less than 2
millivolts across the 16 ohm output; with volume at maxi-
mum, it should not exceed 40 millivolts at this point,

Sometimes, the magnetic field around the PA-774 trans-
former may cause some vibration of the cover which is
audible as a buzzing sound. This can be eliminated by
placing a small wedge of fibreboard or wood on top of the
transformer, between it and the cover.

Distortion

If distortion is encountered, the first thing to do is to
make sure that all inputs and outputs are properly con-
nected and properly functioning. If the leads to a loud-
speaker have frayed cables and touch several screws simul-
taneously, this can be a source of distortion. If a ceramic
cartridge is inserted into the magnetic cartridge input (or
if a tape amp goes in the tapehead input) there will be
overloading of the input and severe distortion.

If the trouble seems to be in the SCA735, then determine
if it is in one channel or both. If in both channels, the only
circuitry common to both channels is that of the power
supply and the 95 ohm resistor in the cathode circuits of
the 6BQ5 tubes.

If only one channel has distortion, tests similar to those
described previously should be used to localize the prob
lem and tubes should be interchanged to see if they are a
cause of it. Inspection of parts on the printed circuit boards
should be made to see if both sides of the circuit are
identical.

Voltage Measurements

The voltage chart shown with the schematic diagram will
be of considerable aid in troubleshooting if there is a
vacuum tube voltmeter or similar test instrument available.
Voltages through the circuit should be compared carefully
with this chart, Deviations up to 20% are not signs of
abnormality, but past this range they indicate a malfunc-
tioning of the circuit at that point. Such measurements can
help to locate defective parts, miswiring, or bad tubes.

Page 19

FACTORY SERVICE AND WARRANTY

This SCA-35 kit is designed to provide reliable perforv
mance for a long time when it has been properly assembled
and operated. It is intended for operation with normal 120
volt AC lines. The guarantee is void if the line exceeds
130 volts AC. A regulating device is necessary if such
excessive line voltage is likely,

To provide rapid, reliable service, Dynaco has authorized
competent, wellaequipped service facilities in the US. and
Canada, in addition to its service facility at the factory.
These stations are authorized to make repairs in or out of
warranty under the terms below. A current list of these
facilities is available on request. It is the owner's respon-
sibility to take or send the unit freight prepaid to the ser-
vice station. Shipment should be via United Parcel Service
or Bus Package Express if possible REA Express is an
alternative. DO NOT USE PARCEL POST. IT IS NOT
A SAFE METHOD OF SHIPPING ELECTRONIC
EQUIPMENT.

Pack the unit properly in the original carton with all
protective inserts, or double-pack it with cushioning be-
tween the cartons. Insure it for $150. Include the follow-
ing information: 1) Your name and complete shipping
address (Post Office box numbers are not adequate); 2)
the serial number from the cover of this manual, together
with a copy of your dated bill of sale; 3) the symptoms,
brief but complete. Specify if the problem is intermittent.

All components in this SCA-35 are guaranteed against
manufacturing defects for a full year from the date of pur-
chase, except tubes, which carry the standard EIA 90 day
warranty. Defective parts will be replaced at no charge if

they are returned prepaid to Dynaco. Local service sta-
tions are not obligated to supply separate parts. If you
suspect a defect in a transformer, cutting the leads too
short for re-use may void its warranty.

Warranties apply only to the original purchaser. They
do not cover units physically or electrically modified, or
abused, or units which are incompletely assembled, or units
on which other than rosin core solder has been used. Units
assembled with acid core solder or paste flux will be re-
turned unserviced.

Dynaco maintains a Technical Services Department to
help you locate the source of, and possibly correct a prob-
lem yourself. You may write or telephone. When writing,
include the serial number and any tests you have made.

If service is required, ship the SCA735 to the nearest
service facility. In-warranty parts will be replaced at no
charge, although a nominal service fee {currently $10)
will be charged for the labor to diagnose, correct and test
the unit to ensure that it meets factory specifications.
Shipping charges to and from the service facility are the
owners responsibility. Units will normally be returned on
a COD basis via UPS. A 90 day warranty is provided on
the service work performed.

After the warranty period Dynaco establishes maximum
labor fees which may be charged without prior approval of
the owner. This current fee is $10, plus the cost of parts
and shipping charges. Dynaco cannot assume responsibil-
ity for service at other than its authorized service facilities.

Dynaco reserves the right to limit the service facility or
the fees to two years from the date of purchase. Dynaco
assumes no liability or responsibility for damages or injuries
sustained in the assembly or operation of this equipment.

PARTS LIST

Parts of similar type which do not change performance may sometimes be included as
a matter of expediency. This will account for slight variations in value or appearance.

RESISTORS PART #
1 50 ohms, 5 watts, 10%-R41 120500
1 95 ohms, 5 watts, 5%-R42 120950
2 2200 ohms (red»red-red), 1 watt, 20%-R39, R40 114222
2 10,000 ohms (brown-black-orange), 1/2 watt, 10%- 112103
R25, R26
2 18,000 ohms (brown-gray-orange), 1/2 watt, 10%~ 112183
R27, R28
1 22,000 ohms (red-red-orange), 1/; watt, 10%-R38 112223
2 1.5 megohms (brown-green-green), 1/; watt, 10%- 112155
R12, R24
CAPACITORS
2 22 nf (.02 mfd) 10%-C15, C16 266223
2 10 nf (.01 mid) 10%-Cll, C12 266103
4 3.3 11f (.0033 mfd) 10%~C5, C10, C13, C14 266332
1 .02 mfd disc-C22 227203
1 Two-section filter capacitor, 50/50 @ 450V-C23 297107
1 Four-section filter capacitor, 60/ 40/ 20 @ 450V; 297227
100 @ 25V-C24
HARDWARE
57 #4 Machine screws 611245
49 #4 Nuts 514245
49 #4 Lockwashers 517205
4 #6 Machine screws 611355
4 #6 nuts 514355
13 #6 Sheet metal screws 612339
12 #8 Machine screws 611455
12 #8 Nuts 514455
12 #8 Lockwashers 617405
10 5%" Control mounting nuts 614065
5 %" Lockwashers 617065
1 Ground lug 639308
1 Pilot light jewel 834004
1 Pilot light jewel spring 712001
1 Rubber grommet 395003
1 Cable clamp 713001
4 Rubber feet 859001

CONTROLS PART #
1 Selector switch 334601
1 Volume control 177254
1 Balance control 157754
1 Bass control 167205
1 Treble control 167504
2 Hum control 147102
3 DPDT slide switch (six lugs) 332201
1 SPST slide switch (two lugs) 331101

1 Fuse holder with rubber washer and circular nut 341002
1 Fuse, 2 ampere, Slo-Blo 342020
2 PEG tone control circuit module (7 leads) 555002
2 PEG input circuit module (5 leads) 555003
2 Silicon rectifier, 500 ma 1000 PIV 544529
2 Mounting wafers for filter capacitors 015001
1 Pilot light socket 386001
1 Pilot lamp #47 526047
2 AC outlet 351001
4 4 socket input socket strip 355004
2 4 screw terminal strip 374004
2 5 lug terminal strip 375001
4 9 pin tube socket 395010
3 Hookup wire (1 each red, green, black)

1 Flat 4- conductor cable 324020
1 Insulating sleeving (black)

1 Line cord with plug 322092
1 Chassis assembly (5 pieces) 711017
1 PA-774 power transformer 464774
2 2-565 output transformer 454565
2 PC 10 circuit board assembly 557010
1 PC 11 circuit board assembly 557011
4 Output tube GBQs/EL 84/7189 (matched) 517005
2 Driver tube 7199 517004
2 Preamplifier tube 12AX7/ECC-83 517003
2 Large knob 764186
3 Small knob 764155
1 Front panel 769015
1 Instruction manual with pictorial diagrams

1 Warranty card 21